Evaporator

ABSTRACT

THE EVAPORATOR IS PROVIDED WITH A DISTRIBUTING CHAMBER WITHIN THE COLD TUBE BRANCHES TO RECEIVE AN INFLOW OF FLUID TO BE EVAPORATED. THE CHAMBER DISTRIBUTES THE FLOW BOTH DOWNWARDLY AND UPWARDLY. THE DOWNWARD PART-FLOW IS DIRECTED TO FLOW AGAINST THE TUBES-BOTTOM AND THEN INTO THE OUTER ANNULAR SPACE BETWEEN THE TANK WALL AND GUIDE WALL. THE FLOW THEN PASSES INTO THE NATURAL CIRCULATION FLOW AND IS DISTRIBUTED ABOUT THE HOT TUBE BRANCHES FROM BELOW. THE UPWARD PART-FLOW IS DIRECTED INTO THE INTERIOR OF THE GUIDE WALL TO MIX WITH THE REST OF THE FLUID.   D R A W I N G

United States Patent Gulich 14 1 Sept. 3,1974

EVAPORATOR Inventor: Johann Gulich, Winterthur,

Switzerland Assignee: Sulzer Brothers LTD., Winterthur,

Switzerland Filed: Apr. 9, 1973 Appl. No.1 349,569

[ 5 7 ABSTRACT The evaporator is provided with a distributing chamberwithin the cold tube branches to receive an inflow of fluid to beevaporated. The chamber distributes the flow both downwardly andupwardly. The downward part-flow is directed to flow against thetubes-bottom [52] US. Cl. 165/1612, 123/33 and then into the Outerannular Space between the [51] Illlt. Cl F 8b 1 tank wall and guidewall. The flow then passes i h Field Of Search 15/l582163i naturalCirculation flow and i distributed about the 165/114 122/3 hot tubebranches from below. The upward part-flow is directed into the interiorof the guide wall to mix Reference; gjgrENTs with the rest of the fluid.

UNITED STAT S 3,576,179 4/1971 Romanos 122/32 10 5 Drawmgngures3,706,301 12/1972 Penfield,.|r .7 l65/l6l r A g e 1 l 16 1 20 1 lqqo l 2l %32 1 1 r l 1 i 1 34 L313 l i 1 3 1 1 1L! V36 5 i K i i L6 l Q l. i 1I I l I i 38 8" l 1 1 1W i l PAIENIEDSEF 31w SlEUIBfZ 3 3 3 7 5 2 m b 8nu U 3 3 3 TV llllll I o FIG This invention relates to an evaporator.More particularly, this invention relates to an evaporator for a steamgenerating plant.

Evaporators have been known to have a vertically oriented pressurizedvessel in which a horizontal tubesbottom is disposed to mount a group ofU-shaped tubes which for hot tube branches and cold tube branches thatextend within the pressurized vessel and conduct a heating medium whilean evaporable fluid flows about the tubes. In many instances, conductingmeans are provided above the tubes-bottom in the region of the hottube-branches to which the heating medium is conducted in order todistribute the naturally circulating fluid along the section oftubes-bottom equipped with the hot tube-branches and to formupwardlybranched-off fluid flows for passage along the hot tubebranches. In addition, these evaporators have also been constructed witha separating wall between the hot tube branches and the cold tubebranches (out of which the cooled heating medium is carried away). Theseparating wall usually extends upwardly and across the entiretransverse area of the tubes group. Suitable means are also provided forfeeding the fluid into the evaporator.

Such an evaporator is known from Swiss Pat. No. 527,390.1n addition,this evaporator is also provided with guiding means with passages abovethe tubesbottom section equipped with the cold tube branches in order todistribute the naturally circulating fluid along this section of thetubes-bottom and to form upwardly branched off partial flows. In thisway, two naturally circulating fluid flows have been produced in theevaporator and delimited from one another in the region of theseparating wall.

However, the heat transfer efficiency of these known evaporators haveusually been limited.

Accordingly, it is an object of the invention to increase the heattransfer efficiency of an evaporator.

It is another object of the invention to cool the heating medium passingthrough an evaporator below the vaporization temperature of the fluidthat is to be evaporated before emerging from the cold tube branches.

Briefly, the invention provides an evaporator of the above type with ameans for conducting or guiding at least part of the fluid flowing tothe evaporator across the cold tube branches as well as with a means fordirecting at least a part of this fluid sequentially against thetubes-bottom, then past the periphery of the tube group and then, afterflowing between the end'edges of the separating wall and thepressure-tank wall, into the space between the conducting or guidingmeans and the section of the tubes-bottom equipped with the hot tubebranches.

The evaporator is thus formed with a preheating zone in the region ofthe cold tube branches for at least a part of the fluid that is to beevaporated. An intense flow along the tubes-bottom section equipped withthe cold tube branches is also produced. Because of the separating wallbetween the hot and the cold tube branches, the fluid flowing in forcedcirculation against the tubes-bottom is compelled, after deviationagainst the pressure-tank wall adjacent to the cold tube branches, toflow onward into the space directly above the section of thetubes-bottom equipped with the hot tube branches. The'preheated fluid isthen mixed with the naturally circulating fluid flowing via the guidemeans. Furthermore, stagnation zones in which any impurities containedin the fluid might otherwise accumulate through evaporation of the fluidare avoided in the region of the heating surfaces.

In one particularly advantageous form of construction, a means isprovided for conducting at least a part of the fluid into the spacebetween the cold-and hottubes branches of the group of U-tubes. Becauseof this, it is possible in a simple way to obtain better utilization ofspace, which leads to smaller dimensions of the pressurized tank.

In accordance with a further form of construction, the means forconducting or guiding at least a part of the fluid are made so that thefluid, during flow toward the tubes-bottom is guided toward and alongthe cold tube branches. To this end, displacing elements are used thatextend parallel to the cold tube branches and are situated between thesebranches to leave unobstructed narrow spaces around the tube branches.

These and other objects and advantages of the invention will become moreapparent from the following detailed description and appended claimstaken in conjunction with the accompanying drawings in which:

FIG. 1 illustrates a vertical section through the lower end ofan'evaporator according to the invention;

FIG. 2 illustrates a view taken on line II-II of FIG.

FIG. 3 illustrates a view taken on line III-III of FIG. 1;

FIG. 4 illustrates a view taken on line IVIV of FIG. 1 and to a greaterscale; and

FIG. 5 illustrates a view taken on line V-V of FIG. 1, and to a greaterscale.

Referring to FIG. 1, the evaporator of a nuclear reactor plant consistsessentially of a pressurized tank 10, a tubes-bottom l and an inflowchamber 4 and an outflow chamber 6 for a heating medium. The heatingmedium, e.g. water under pressure, before entry into the inflow chamber4 cools a reactor core as is known and, after giving up heat in theevaporator, flows back to the reactor core. The two chambers 4, 6 aredelimited by the tubes-bottom l, by a separating wall 3, and by aspherical bottom 2, to which are connected a connector 5 for the inflowof heating medium, and a connector 7 for the outflow of the heatingmedium. In addition, tubes 8,9 are tightly fastened in thetubes-bottom 1. These tubes 8, 9 are connected, as is known, by bows(not shown) to form a tube grouplZ of U-shaped tubes so as to conductthe heating medium from the inflow chamber 4 to the otuflow chamber 6.As shown, one set of tubes forms hot tube branches 8 connected to theinflow chamber 4 while the other set of tubes forms cold tube branches 9connected to the outflow chamber, 6. The pressurized tank 10, as isknown, merges at the top into a hemisphere. (not shown) which isconnected to a connector to remove the steam produced from a flow ofwater passing around the tubes 8, 9. The tube groups 12 is surrounded bya tubular guide-wall 16 which defines an annular space with thepressurized tank 10 in which the naturally circulating water to beevaporated flows downward.

A means for guiding the water to be evaporated is positioned above thesection of tubes-bottom equipped with the hot tube branches 8. Thismeans is in the form of a flat sheet of metal 45 formed into a surfaceof a half cone and tightly connected by a curved rim to the lower end ofthe guide-wall 16. The rectilinear edge of the sheet 45 is, except for arectangular cut-out opening 46 (FIG. 3), tightly connected to aseparating wall 20 which runs upward from the tubes-bottom l and extendsover the entire transverse area of the tubes-group 12 (FIG. 2). Themetal sheet 45 is provided with passageway openings, through which thetube branches 8 extend with a clearance. In this way, the water flowingdownward in the annular space between the pressurized tank 10 and theguide-wall 16 passes over the section of tubes-bottom 1 equipped withthe hot tube branches 8, and becomes divided between these branches 8and the sheet 45 into partial currents.

The separating wall 20 is not situated in the middle of the spacebetween the hot and the cold tube branches 8, 9 but is shifted towardthe cold tube branches 9. Because a portion of the tubes-bottom 1 isthus not equipped with tubes, which results in an unequal distributionof the water at the hot tube branches 8, stumps 47 (shown hatched inFIG. 2) are positioned in the region of this section and fixed on theunderside of the metal sheet 45 to simulate the tube branches 8.

A four-cornered box 21 is provided in the lower region of the tubesgroup 12, between the tube branches 8 on the one hand and the tubebranches 9 on the other hand. This four-cornered box 21 extendstransversely through the group 12 as far as the guide-wall 16. The twoends of the box 21 are fastened to connectors 22, 23 respectively, whichpass through the wall of the pressurized tank 10, and join conduits 24,25, respectively. These conduits 24, 25 are connected to a common pump11, which supplies the evaporator with the water that is to beevaporated, e.g. taking the water from a condenser of a steam-turbineunit in which the steam produced by the evaporator is expanded. A numberof openings 30 are formed in the separating wall 20 in the region of thefour-cornered box 21 and aredistributed along the length of the box 21to connect the box 21 with a distributing chamber 31. The distributingchamber 31 is delimited above and below by two metal sheets 32, 33 whichrun from the separating-wall 20 as far as the guide-wall 16, and aretightly welded to these walls. As in the case of the metal sheet 45,passageway openings 33 are provided in the sheets 32, 33 for the passageof the cold tube branches 9 with a clearance so that the water to beevaporated is able to go through these openings out of the chamber 31.The lower sheet 33, delimiting the distributing chamber 31, runs fromthe separating wall 20 slightly upward whereas the upper sheet 32 runshorizontally. This results in a flow section that decreases outwardlyfor the distributing chamber 31.

A metal sheet 38 is disposed in parallel to the lower sheet 33 near thetubes-bottom 1, and likewise extends from the separating wall 20 andmerges via a curved end into the lower rim of the guide-wall 16. Thesheet 38 also has passageway openings like sheet 33. In this way, aspace is formed between the sheet 33 and the sheet 38 which housesdisplacement or supplanting elements 36 (FIG. 4) which extend over theentire height of the space.

Referring to FIG. 4, the elements 36 are of hexagonal cross-section, thesides of the hexagons being alternately straight and concave. Theelements 36 are dimensioned so that a narrow interstice 41 is leftunobstructed between the concave sides and the tubes 9. Moreover, narrowinterstices 42 are formed between the straight sides of adjacentelements 36 for the purpose of taking into account heat-expansion. Inorder to center the elements 36, two longitudinal beads 40 are providedat the ends of the concave sides respectively, to bear against the tubebranches 9.

Referring to FIG. 1, a wall 37 is disposed in parallel to and above theupper delimiting wall 32 of the distributing chamber 31. This wall 37 isconnected tightly to the upper end of the separating wall 20 and iswelded tightly to the guide-wall 16. Displacement elements 35 are placedin the space formed by the two metal sheets 32, 37. These displacementelements 35 are made and arranged similarly to the elements 36 describedabove.

Referring to FIG. 2, the guide-wall 16 extends downward as far as thetubes-bottom 1 over a range of 45, in each case measured from theseparating wall 20, to form two wall-parts 39. This results in a 90opening between the two wall-parts 39. As a result, the water whichflows through the openings in the metal sheet 38 passes through theopening between the wall-parts 39 into the annular space between thewall-parts 39 and the adjacent pressure-tank wall. Thereafter, the watercan flow into the space between the metal sheet 45 and the section oftubes-bottom 1 equipped with the hot tube branches 8 and can becomemixed with the naturally-circulating water.

The center of the tubes-bottom 1 is provided with a blind hole 48. Asshown in FIG. 5, the bottom of the blind hole 48 communicates with anupwardly-slanting bore 49 to which a conduit 50 is connected. Theconduit 50 runs along the tubes-bottom 1 and out of the evaporator (FIG.2), for the purpose of removing sludge.

In the operation of the evaporator, 90 percent of the total fluid orwater to be evaporated is, for example, fed through the pipes 24 and 25to the four-corners box 21. The fluid then flows, by way of the openings30, into the distributing chamber 31. Approximately half of the quantityof fluid, 45 percent that is, then flows, forcibly actuated, through thegaps 41 and 42 of the tube branches 9 and between the displacementelements 36 downward towards the tubes-bottom 1. After flowing throughthe passageway openings in the metal sheet 38, the fluid, whileintensively washing the section of the tubes-bottom 1 equipped with thecold tube branches 9, flows radially outward to the periphery of thegroup of cold tube branches 9, and arrives, by way of the 90 opening,between the wall-parts 39 in the annular space between the wall parts 39and the adjacent wall of the pressurized tank. The fluid then flows inthis annular space along the periphery of the tube group and afterpassing the end edges of the separating wall 20 arrives in the spacebelow the metal sheet 45. The other half of the fluid flowing into thedistributing chamber 31 flows between the elements 35 upward in adirection toward the cold tube branches 9. After flowing through thepassageway openings in the sheet 37 into the space enclosed by the guidewall 16, the fluid mixes with the remaining fluid that flows, by way ofthe sheet 45, into the space enclosed by the guide-wall 16. Theremaining of the fluid that is to be evaporated is fed through aconnector into the annular space between the pressurized tank 10 and theguide-wall 16 in a way known of itself, approximately at the level ofthe fluid to be evaporated.

The slope of the metal sheet 45 should be made such that the section ofthe tubes-bottom l equipped with the hot tube branches 8 is washed withsufficient speed as far as the region of the blind hole 48. If apreheating of the fluid that is to be evaporated occurs at the cold tubebranches 9 sufficient to bring the fluid up to saturated-steamtemperature, then it is possible for so great a formation of steam tooccur between the metal sheet 45 and the tubes-bottom 1, that the slopeof the sheet 45 may be zero or even negative.

A baffle (not shown) can be provided in the annular space between thepressurized tank 10 and the guidewall 16 adjacent to the cold tubebranches 9 to extend 180 about at the height of the section line IVIV inFIG. I. This baffle would prevent the preheated fluid emerging from themetal sheet 38 from flowing upward into the annular space.

What is claimed is:

1. In an evaporator having a pressurized tank, a horizontal tubes bottomextending across said tank, a group of U-shaped tubes mounted in saidtubes bottom and including hot tube branches and cold tube branches forconducting a heating medium therethrough, a separating wall between saidhot tube branches and said cold tube branches and extending across saidgroup, means for feeding a fluid to be evaporated into said tank, andmeans above said tube-bottom and between said hot tube branches fordistributing a naturally circulating flow of the fluid flowing acrosssaid tubes bottom upwardly into a plurality of part flows; first meansfor guiding at least a part-flow of the fluid fed into said tank acrosssaid cold tube branches and second means for directing at least aportion of said part-flow sequentially against said tubes-bottom pastthe periphery of said group of tubes, and into said means above saidtubes-bottom.

2. In an evaporator as set forth in claim 1, said first means beingdisposed between said hot tube branches and said cold tube branches.

3. In an evaporator as set forth in claim 1, displacement elementsextending between said cold tube branches in parallel to define narrowunobstructed spaces therebetween for the flow of fluid therebetween.

4. An evaporator comprising a tank;

a horizontal tubes-bottom extending across said tank;

a group of U-shaped tubes mounted in said tubesbottom to define hot tubebranches and cold tube branches;

a separating wall between said hot tube branches and said cold tubebranches, said wall extending across said group of tubes;

a guide wall surrounding said group of Ushaped tubes and spaced fromsaid tank to define an annular space therewith;

a first means for guiding a delivered flow of fluid across said coldtube branches;

second means connected to said first means for directing at least aportion of the delivered flow downwardly along said cold tube branchesagainst said tubes-bottom and outwardly into said annular space; and

a third means between said guide wall and said separating wall and abovesaid tubes-bottom for receiving and distributing a flow of fluid fromsaid annular space into a plurality of part-flows of fluid upwardlyalong said hot tube branches within said guide wall.

5. An evaporator as set forth in claim 4 wherein said first meansincludes a box between said hot tube branches and said cold tubebranches for receiving an inflow of fluid and a pair of sheets extendingfrom said box across said cold tube branches to define a distributingchamber therebetween for receiving fluid from said box.

6. An evaporator as set forth in claim 5 wherein said second meansincludes a sheet extending from said separating wall to said guide wallacross said cold tube branches and between said distributing chamber andsaid tubes-bottom, said sheet forming a clearance with each cold tubebranch for directing a part flow of fluid against said tubes-bottom.

7. An evaporator as set forth in claim 6 wherein said third means is asheet forming a clearance with each hot tube branch.

8. An evaporator as set forth in claim 6 which further comprisesdisplacement elements between said cold tube branches and definingnarrow spaces therewith for passage of fluid therebetween.

9. An evaporator as set forth in claim 4 wherein said second meansincludes a sheet extending from said separating wall to said guideacross said cold tube branches above said tubes bottom, said sheetforming a clearance with each cold tube branch for directing a part flowof fluid against said tubes-bottom.

10. An evaporator as set forth in claim 4 further comprising fourthmeans connected to said first means for directing another portion of thedelivered flow upwardly along said cold tube branches to mix with thepart-flows of fluid passing through said third means within said guidewall.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3, 33,5 Dated Sep em er 3, 197

Inventor(s) Johann Gulich It is certified that error appears in theabove-identified patent and that said Letters Patent are herebycorrected as shown below:

Insert the priorityparticulars to read as follows:

- --'January 9, 1973 Switzerland 252/73.

Column 2,flin e 51, "otuflow'f should be --outflow--.

Signed and sealed this 3rd day of Deeeraber 1974.

' (SEAL) Attest:

IIcCOY M. GIBSON JR. C IIARSHALL DANN Attesting Officer. Commissioner ofPatents FORM PO-IOSO uo-es) 4 USCOMWDC 6 5. U.S. GOVERNMENT PRINTINGOFFICE: I", O-BiE-J Sl.

